Blackbody Radiation of Boiling Water

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Discussion Overview

The discussion revolves around the blackbody radiation characteristics of boiling water in a coffee mug, exploring whether the mug can be approximated as a black body for infrared (IR) radiation. Participants consider theoretical methods for calculating expected peak emissions based on quantum mechanics and the vibrational modes of water, while also questioning the applicability of Wien's Law in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that a coffee mug could be considered an approximate black body for IR radiation due to its insulation, but expresses uncertainty about this assumption.
  • Another participant questions the applicability of Wien's Law, noting that it relies on the object being a black body, which leads to a discussion about whether boiling water can be accurately modeled as such.
  • A different viewpoint suggests that while the coffee may not be a perfect black body, it could still exhibit dominant black body characteristics despite additional absorption/emission effects due to its chemistry.
  • Participants discuss the potential use of quantum mechanics to predict peak emissions based on the vibrational modes of water, indicating a desire for a theoretical approach beyond empirical measurement.
  • One participant suggests conducting experiments in a controlled environment, such as a dark box or Faraday cage, to minimize additional emissions and focus on black body characteristics.

Areas of Agreement / Disagreement

Participants express differing views on whether the coffee mug and boiling water can be accurately modeled as black bodies. There is no consensus on the applicability of Wien's Law or the best approach to calculate peak emissions, indicating ongoing debate and uncertainty.

Contextual Notes

Participants acknowledge limitations in their assumptions regarding the black body model and the complexities introduced by the chemistry of the coffee. The discussion also highlights unresolved mathematical steps in applying quantum mechanics to predict emissions.

stanli121
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I was thinking about this the other day and I wanted some other input on the matter. Cups of boiling water (I was thinking about coffee) give off gobs of IR radiation at both near and mid wavelengths. Could I think of a coffee mug as an approximate black body for IR radiation? The insulation of the mug seems to make it possible but I'm really unsure.

Second, is there a decent theoretical manner to calculating the expected peak emissions of hot coffee in a coffee mug? I'm getting very curious and I could always use an IR spectrometer but I was wondering if there's any method via QM based on vibrational modes of water at a given temperature to predict the peak emissions? If the cup can be modeled as a blackbody Planck's Radiation Law solves my problems but I have a hunch it won't be that simple.

Lastly, my understanding of this physics is at the advanced undergraduate level so I should be able to understand any math/theory people throw out for this. Thanks a lot in advance mates!
 
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stanli121 said:
I was thinking about this the other day and I wanted some other input on the matter. Cups of boiling water (I was thinking about coffee) give off gobs of IR radiation at both near and mid wavelengths. Could I think of a coffee mug as an approximate black body for IR radiation? The insulation of the mug seems to make it possible but I'm really unsure.

Second, is there a decent theoretical manner to calculating the expected peak emissions of hot coffee in a coffee mug? I'm getting very curious and I could always use an IR spectrometer but I was wondering if there's any method via QM based on vibrational modes of water at a given temperature to predict the peak emissions? If the cup can be modeled as a blackbody Planck's Radiation Law solves my problems but I have a hunch it won't be that simple.

Lastly, my understanding of this physics is at the advanced undergraduate level so I should be able to understand any math/theory people throw out for this. Thanks a lot in advance mates!

I don't understand why you wouldn't expect Wien's Law to give the correct answer?
 
Doesn't the Wien Law rely on the object being a black body? If the coffee could be considered a black body then this would be a relatively simple thing to figure out but that's where I'm stuck -- whether or not this can be accurately modeled as a black body!
 
stanli121 said:
Doesn't the Wien Law rely on the object being a black body? If the coffee could be considered a black body then this would be a relatively simple thing to figure out but that's where I'm stuck -- whether or not this can be accurately modeled as a black body!

Why wouldn't it be a black body? It's going to have additional absorption/emission depending on the chemistry but it'll still have the black body as the dominant emission. If you don't want to worry about additional emissions then do your experiment in a dark box+faraday cage
 

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